Grid controlled storage tubes



March 11, 1958 Filed June 29, '1951 s. v. FORGUE GRID CONTROLLED: STORAGE TUBES s Sheets-Sheet 1 T m/41 //VPU7 S. V. FO RGUE GRID CONTROLLED STORAGE TUBES March 11, 1958 3 Sheets-Sheet 2 Filed June 29, 1951 EQRQQNKQ LI TT IIIITIIIIHI INVENTOR qWhEREvSXQR? gww March 11, 1958 s. v. FORGUE 2,326,714

I GRID CONTROLLED STORAGE TUBES Filed June 29, 1951 5 Sheets-Sheet 3 N EY Stanley V. Forgue, Cranbury, 1., assignor to Radio inparticlller to ag ube in h h a i lt l 1 15! 19 t gt i mighti a e 8 gif 'to be clearly seen by the fobs'eryer or consist of signal United States Patent 0 "ice 2,826,714

Batented Mar. 11, 1958 l Beams at he tasaetaria e at iasset t e E %g@ as r fleqtsd be {m =2! b th -a en tsxe ont ae l r nws e ae c ctedw pr ide tube be 2552M. GRID ooN Ro LED sromon TUBES t e care i .3 ea

Te: Exc te? re e ch .eeti e e rest w i? t Corporation of America, a corporation of Delaware Application June 29, 1951, Serial No. 234,202

M EQ QQEYF Q lIRE em; he tei 1$ mvent q r tes o e ec ro d sch rge iPb sa 5 T e we e es wh b o' 'e as a charge na 'emo ere? slct qds within the tube and utilized to provide output signals at a later time.

Such storage tubes have great utility in applications e saislesl 3 .2199 at yt stsw 32 e su as radar and sy vih i iq m fiq fi er li iii rg l i a, sss igga view 9 #2 1 9 electrically, and must be arranged to provide a visible patd evi: e ps ed as a storage tube accordanc tern to an observer. Normally, such information in yenton. l V

.2 ia'sg g tgat s Wing 9.1? sever l mee i in many cases the incoming signals'are either too rapid t e was at 9 g P l 9ndary material.

. ulses, which must be arranged relative to each other jkgat e16? prqvid? 3 9 1 9 p s ture on an oscilloscope sgr een.

It "is often desirable that signals of short duration be 0" fii' i g efi e iisher aesterea ae a ase carefully u s or th se h f m a g g s te P r offiiiS'ditiiH 'ofFi ure 1: eine 3 the gselllgseppe s e u tly g= 9 Figure 6 is a s c i al yie 4 Bionic stgt ee t all of the picture to be put down. AccordinglyQit is i a g ii]; 1? W are used.

ltis'an object of my invention to provideastorage tube for the storage of incoming signals to be used at a later time. "It isanother objectof my invention'to-provide asto-rage tube having '-a target electrode of a nature that incoming signals e-an-be-stored thereon for -any:length of time desired by an observer. 1t isafurther object of :my invention -to provide a storage tube hayinga target elecvtrode with long=storage time characteristics. It is also an object of my invention to provide a storage tube-haying a target electrode upon which incoming signals can be established and can "beerased atlwill by an observer.

Specifically the invention is directed to anelectrondis -charge device .usedfor storing signals .to .be subsequently -nsed. Thetubeincludes a-target electrode formedof a foram-inoussheet havinga dielectric .layer on the surface thereof. 'Meansareprovided to-store a charge pattern on a t mm to ihwetfl one:surface -of -the tar-get sheet in accordance with-signal i 23 :2 i g g s d g g =-inormation.directed-intothe tube. Abeamofclectrons, m PM A surface of thejwirgs ofithe metal O formedaby anelectron gun .-w1th1ntthe-.tube, 1s used toread F g w w gp the stored charge pattern without erasing the :pattern :stored 0114116 :targehelectrode. fine-form of :the tnbez has a wniting gun on ,one =side-of .-the 'foraminous target telectrode for. putting down a charge distribution on the surface of the tar get electrode inaccordancemith signalstapplied to che control grid. of-thewritin-g gun. On the opposite sideofi the target is arranged a reading gun for providing an electronbeamof :low velocity, which is scanned. over "the. opposite surface -.of .thenforaminous .-.-.ta1: get.e l ectrode. 'Theqreading aheam ewillgtend to :passthrough. the openings ,ofathe.rtarget-adiacentz o :posi-tively-pharg d ar i-target .aurtace zand he complete y 91 for providing a pair 3 trode 16 and provide an output signal corresponding to the charge pattern on the target.

Essentially, the writing gun 25 is of a conventional type and consists of a cathode 25, a control grid 28 and an accelerating grid30. The cathode 25 is essentially a metal tube closed at theend facing target 16, which end is coated with electron emissive material to provide a source of electrons. The electrons are formed into a beam by electrodes 28 and 30 and directed toward target 16. Between'gun 24 and target 16 are mounted additional electrode structures consisting of a long metal tubular electrode 32, which maybe connected to accelcrating electrode of the gun. Between electrode 32 and target 16, is mounted a screen or collector electrode 34, supported by a ring 36 and closely spaced from the coated target mesh 18.

The electron beam of gun 24 is, focused to a well defined'spot on the surface of thetarget 16 by a focusing coil 38 coaxially mounted aboutthe tube envelope 10. The focusing operation of coil 38 is well known and is not described in detail here. Also, surrounding the envelope 10 and adjacent gun 24 prisingtwo pairs of oppositely disposed magnetic coils of deflecting fields at right angles to each other. As is well known, the coils of each pair of coils are connected respectively in series to a source saw-tooth'voltages for providing respectively line and frame scansion of the beam of gun 24 over the surface of target 16. The several electrodes of gun 24 are connected to a source'of potential through a voltage divider 33, to provide the different voltages required for gun operation. Control grid 28' and accelerating grid 30 are coupled to cathode 25 through voltage sources and 37 respectively. f

The reading gun 26 is similar to gun 24. The cathode of gun 26 (not'shown) is operated at ground pois a neck yoke 40 com tential which is the potential of the metallic screen 18 of target 16. The electron beam of gun 26 is accelerated to a velocity of several hundred volts by an accelerating electrode 44. An extension of coil 38 provides a focusing field between gun 26 and target 16 to bring the electrons of the beam to a fine spot on the surface of target 16. A tubular electrode 46 provides a substantially field J free space between electrode 44 and target 16 and prevents the glass envelope wall from charging up during tube. operation. maintained at the same potential of the accelerating grid 44. A neck yoke 45 represents deflecting coils for scanning the beam 'offg'un 26 over the surface of 'target 16, in a well known'manner.

Adjacent target 16 and between gun 26 and the target is an open screen 48- supported by a ring 50. Screen 48 is of high transmission and is maintained at around 180 volts above ground potential during tube operation. Since the metal screen 18 of target 16 is at ground potential, screen 48 provides a uniform decelerating field in front of the target, to slow down the beam of gun 26 to essentially zero velocity. The electrons of the beam approach the dielectric surface of target 16 with very little energy. Due to the velocity range of the electrons in the beam some of the beam electrons will strike the coated surface of screen 16 with a volt or so of energy. Under these conditions the secondary emission from the dielectric coating is less than 1, and the dielectric coating will be driven slightly negative to 21 volt or so below ground potential. At this point, all of the beam electrons are reflected back toward gun 26. Due to the focusing field of coil 38, these reflected electrons will travel back toward the positive accelerating grid 44 along substantially the same path that they took on their approach to target 16. The reflected electrons. will strike the surface of accelerating grid 44, which is normally treated :to providea high secondary electron emission. This secondary electron emission is pulled Electrode 46 may be lector screen 34 is operated at around .then, the electron beam of gun 24 is through the several stages of a multiplier section 52 to produce a many-fold amplification of the beam electrons, the secondary electrons of the multiplier are collected by a multiplier collector electrode 54. The details and operation of the particular multiplier shown in Figure 1 are fully set forth in U. S. Patent 2,433,941 of P. K. Weimer. The several electrode parts of gun 26 as Well as the electrodes 46 and 48 are adjustably connected, as shown in Figure 1, to the voltage source 33.

OPERATION 1 Writing As indicated in Figures 1 and 2 the metal screen 18 of the target electrode is maintained during tube operation at ground potential. To write a signal pattern on target 16, the cathode of gun 24 is held at around 300 volts negative with respect to ground potential. C01- 150 volts pos- In this manner, accelerated to a high velocity by the potential of the collector screen 34, which is substantially 450 volts positive with respect to the cathode electrode 25.

As the beam of gun 24 is scanned over the dielectric surface of target 16 the electrons of the beam will strike the target surface at high velocities. The energy itive with respect to ground potential.

V of the electrons will be between 300 and 450 volts. The

electrons striking the silica film 22 of target 16 will initiate a secondary electron emission from the bombarded area greater than the number of the electrons striking the area.

There is shown in Figure 3, the relationship between this ratio of the number of secondary electrons leaving a dielectric surface to the incident bombarding electrons. The vertical axis of the diagram of Figure 3 42. At this voltage, as many secondary electrons leave the bombarded surface as incident electrons strike the surface. The curve indicates that the secondary emission ratio increases with an increase in the energy of the bombarding electron beam to a certain point, fromwhich the'secondary emission decreases with further increase of beam energy. Where curve 41 initially crosses line 42 is known as the first crossover point.

The secondary emission from the dielectriecoat 22 of target 16 is collected by'the mesh screen 34. The

: bombarded areas of target 16 will be rapidlydriven positively by the secondary emission therefrom and will beraised to a positive potential close to the 150 volt potential of screen 34.

A bombarded area of the dielectric surface of fihn 22 will not be driven above the potential of screen 34, since the secondary electrons leaving the bombarded dielectric film 22 will be collected by screen 34 only as long as the collector screen is more positive than the surface of the silica film 22. If a bombarded area of silica film 22 tends to go above the potential of collector screen 34, screen 34 will then present a negative field to secondary electrons leaving the bombarded areas. These secondary electrons will be reflected by this negative field and fall back onto the surface of target 16. In this manner, the collector screen 34 establishes an equilibrium potential to which the bombarded portions of the dielectric film 22 are driven by the electron beam of gun 24.

To write a signal pattern on the dielectric surfaces of target 16, the beam of the reading gun is first scanned on the target 16 to drive all portions of the dielectric film 22 substantiallyto ground or gun cathode potential.

A pattern of charges may then be established on the a dielectric surface of the fcraminous .targetlfihy modulating the electron beam ,of gun .24, .as fitiis being scanne over the surface of the target. 'Forexatnttlajhfithliflg signals to be stored are first amplifiedby an amplifier tube 56 to provide signal voltage pulses which are applied 5 tbetween the cathode '25 and the control grid 28 ofgun 24. Ifthe grid zs ispreviously held ne'gative to cathode 25, to cut off the electron beam, any incoming signal voltages applied-to grid 28 will pulse -the grid above 'its cutoif potential by varying amounts to provide modulation of the eleciron'beam in accordance with the signal pulses applied. 'Such modulation-of an electron beam ris-well known. Themodulated beam, as it is scanned .overthe dielectricsurface of target 16, at each-elemental areastruck by the'beam willdrive the dielectric target :toward the equilibrium 'potential established by collector screen 34, in accordance *with the operation described above. The areas of the dielectric -target-film 22, not "struck -by the "beam will remain at substantially ground -or at the potential ofthe cathodedfgunZG. "Thus -the 'writing beam of gun 2'4 establishes'a-pattern of "dificr- \ently charged areas on the target surface. "This charge pattern,'in the direction 'of beam scansion and at each elemental target portion, corresponds to the successive signal pulses applied'to the writing gun control grid as" the beam scans the target area.

Reading .After the charge pattern hasbeen establishedtby gun 24 on target 16, .gun .24 may be turned Keit and ,the

pattern will remain on .the targebbecause of ,th thighcin- .su1atingproperties of thesilica coating-22.

aportion of. the target .16 of Figure .1. Thepositiv area established .on the surfaceof target ,16 by the beam-,of gun 24 provide positivefields which extend ihl'ough the adjacent openings of the screen. to reduce, those areas, the negative reflecting field originally established on the dielectric film 22 by'the beam of gun 26. In

Figure 4,,for example, it isassumed that the areawhllafiketed byyA has. been charged-positively by the writing-;beam. The positive field of this charged 'areaextends through the openings oftscreen 18. As the beam Qf.gfln;;26 scans across the .target portion A, it will see theaposifive-field and will beidrawnthroughrtheopenings inithe .screenw18. In areas 13 andUCof ,FigureA, itjs assumed that no positive charges have been establ shed hy-,- the .beam of gun 24011 the target. In these unchargefl'tareas, the beam of gun '26 willbe reflected rbaoktowalidlgun 2 6. Thus, as the .beam of gun 26 isjscannedover the charged target, 16, .thevbeam will he.1robbed of electrons in those target portions which have a positive charge :thereon, but willbeatotally reflected by the negativee'areas or unchargedvareas-of thetarget surface. .111 thismanner, the electron beam returning to gun,2 6 will bemodulated in accordance with the charge-patternestablishedjhy'the beam of gun 24 on .target16. This modulated return beam is amplified by the multiplier section 52 to provide a voltage signal pulseinthecircuitof multiplierccollector electrode -54. This voltage pulse-is amplified by any --we1l known means, such ,asia circuit including -an-.amplifiertube-SS, the control grid of which is coupled to :the .multiplier;collector electrode 54. "The-electronsofthe beam. of gunlflfi, :which penetrate through screen 18 .zthecpositi-vely charged areas, are urged toward the positive collecting screen '34, where they arermostly collected.

The output signal of the tubes of Figure 1 can tbeeused (to :modulate the b amof an oscilloscop tube or; atele- -.vi-sion picture-(tube .upon "the vfluorescentscreen ofvw-hich rthe -chargepattern can be observed .as a emtesponding visualcpattem. Thescanningofthe-hearntot the oscillo-- scene tube mu h synchronized with th eanuing theih ani otggunifi .Emsiaga V flzltdsdesir-ahle toibe :able 'to-erase-the charge :pattern from target 16 eithercompletely :orpartiallyinnrderrto .apply-additionalinformation tothe target. i-Atsatisfactory method of providing erasure .of :the chargepattern. :is no ground the QCQHQCLOESCLCEB 34 (Figure :2) tandiscanterget 16 with the full writing;beam,:inzthe-.manner.described. The writing beam will stiiltstrike all portions of the dielectric surface 22 of target 16, at an energy above first crossover. The-secondary electrons fromallareas of the dielecnic-film n are now-reflected back on 'the target surface by :the ne gati-ve field =of collector screen 34 and will establishall :ofthe dieleetric-film 22 scanned bythe ewriting' -beamat groundpotential. "Thismethod'of erasure :is effectively that of-changing the equilibrium potential of 'the dieleetiic surface of 'target "16 from .150 volts positive -to ground=potential. After erasing the charge-pattern, collectorscreen 34may'be resetat 150 volts positive with respect to ground and a-new set of signal-scan be use'dtoestablishanother pattern of positive charges on target '16.

Erasing -B .Another-methodof reflecti g erasure. of the harge-ya .te nentarget .16 is .thatin which the potent al o collecto screen 5.4 isredueedto a poin .wher trea ing beam-ele trons tron; .2 whichp netr t scr n 16, will b refl ct d ha k on o the-s r e qf't targe :16- .Ih

- writing gunle is t rned-oft :LF gure2) :dng misspr tion. Withthe potential-of sereenfi elo groun tor example, the r ding beam electrons will .bestume .baeltqontothetarge suriae .Alsoanyiseecnd ry mi siontfrnm the target will be suppressed hyz h sat r screen. 34. lhusthe eadingt amre eetron z-ran dly riv the rf .oiltarge r 6, ac ng th screen -13), to an equilibrium potential egual substantially to that of ground.

' .rSl w era r A rtaethod'of slow erasure by the readingbeam is also possible. The potential-ofeollector screeii 34 is lowered to a-spoint where only a portionof the reading'beam is reflected backonto the targetscreenlfi. it the reflected portion of the reading beam 'is-smajll then the reading beam electrons --fa-llin-g 'backon'to the target l o will only slowly erasethe charges established on the tar get. In this operation, the writing beam can *be :used'to reestablish any desired portion of thech-arge pattern, whilenndesired portions will slowly disappear.

This operation of -slow erasureis ofvalueinsystems such as radar. Insuch-anapplication, the scanning yoke 500f gun =24 is arranged to provide aPPI type scanning of the beam of gun 24 pverthe target surface 16. This type of scanning'is-wellknown 'andis synchronized with the radar antenna ,;so thatthe beam of gun24 may put downon the targetsurface a'c'harge pattern in accordappe with the incoming radar signals. The output signalof the tube is applied to the controlgridofanoscilloscope tube to provide-avisual picture ofthe,charge,pattern on target 16. "with the described method .of slow erasure, the picture of moving objects on the radar oscilloscope screen 'will gr adually disappear over an adjustabledength of time, 'whilethe picture-of stationary objects, which are repeated, will be retained on theoscilloscope picture.

Selective ,erasure I-Parts of-the chargepattern-onwtarget 16may'be erased selectively by scanning the beam of gun 24 only over vportions of the target surface which are to' be erased. Thiscan be accomplished by manual-control-of the hori- ,ze al .alld vertical deflecting fields rot-yoke #40. ':An operator, by :watching the-picture :ofcrthe charge -patterr1 eneansesc lloscope tube,;canzwith time-practice, direct the Mamet gun.24 tonny portionot the taFgt1WmCh i91Q potential. or retained on the surface of target 16.

target 16 can be maintained sirable that this leakage through thesilica film A aszefiia.

beerased; For this operation, the erasing conditions of the tube must be established, to use either'the' writing beam electrons or the reading beam electrons for erasing.

When gun 24 is used, as described above for erasing the charge patternpthe beam also may be so defocused ,that the electrons of gun 24'reach the target not as a beam, but as an electron spray, covering the whole target area. This method of erasure does notrequire scanning on target 16 for adesired length of time. Also, if the foraminous conductor can 1 reflect the reading electron gthe writing side.

tion 1 signal pattern on His read for a considerable length of time, the pattern becomes somewhattindistinct. This is due to the conditions existing during tube operation, in which electrons from the reading beam fall on the charged areas of target 16 and gradually ,drive them down in potential. Also, there is a small amount of current leakage through the silica film 22 between the grounded wire screen 18 and the positively charged areas of the film, which must be considered if storage times in excess of a few hours are valued. It is thus, desirable often to sharpen the image by restoring the charge pattern to its original condition. Both of these results have been accomplished by'periodically raising'the cathode of gun 24 to ground potential accompanied by a corresponding increase in the potential of the other electrodes of gun 24 (Figure 2). With screen 34 held at its collecting potential of 150' volts, the beam of gun 24, is scanned over target 16. The beam will strike the charged areas of target 18 at above first cross-over to drive them to the equilibrium potential of screen 34. Also the beam will strike the areas of target 16, which have not been written on, below first cross-over to drive them back to ground In this manner, the charge pattern is restored Holding B Another method of holding or restoring the charge pattern on the target is possible with the cathode of gun 24 set at about 300 volts negative with respect to ground and with screen 34 set at 150 volts positive with respect to ground (Figure 2). By directing the writing beam at the support ring 20 of target 16, the beam of gun 24 will strike ring 20 at above first cross-over to. provide a cloud of secondary electrons of relatively low velocity. Those areas of the target, which have been written upon will be at a potential greater than first cross-over above the potential of ring 20. Thus, secondary electrons from ring 20 will strike these areas at potentials to initiate a secondary emission therefrom greater than unity. This will restore the charged areas to equilibrium potential, which is substantially that of collector ring 34. Those secondary electrons from ring 20 falling upon the unwritten or uncharged portions of target 16 will land thereon at below first cross-over and will maintain them at ground potential. In this manner then, the original 'charge pattern can be restored by periodically striking ring 20 with the high velocity beam of gun 24.

The tube of Figure 1 may be operated under slightly different conditions than those described above, to provide somewhat similar results. For example, screen 18 of at any potential, during tube operation, between ground and first cross-over. However, it is set as low as possible so as to minimize charge leakage between the surfaces of the silica coating 22. It is de- 22, be at a minimum. In practice it is low enough to allow a storage time of a few hours or less. .The invention 'need not be confined to magnetic focusing and deflection of the .electron beams, as both electrostatic focusing and deflection may be used instead. Target screen 16 may In" this case the be set at a potential to just when there is no charge on OPERATION 2 'The tube of Figure 1 may also be operated under different conditions than those outlined above in Opera- The collector grid 34 is set at substantially volts positive; with respect to ground (Figure 2). In writing the charge pattern on target 16, the reading gun is first scanned over the target surface to drive the dielectric coating 22 tosubstantially cathode or ground poten tial. The writing gun is operated with a cathode potential of nearly -500 volts negative with respect to ground. The writing beam is scanned over the target surface while the input signals are simultaneously applied to the con trol grid123 of the gun [to modulate the Writing beam.

Wherever the modulated Writing beam strikes the target surface it will charge the surface of the dielectric film to substantially collector screen potential of around 20 volts positive, while the areas not struck by the writing beam will remain at substantially ground potential. The establishing of the charge pattern is due to secondary emission from the target surface in .the manner described above. The reading takes place in the normal manner described above. ,4 1

v Erasing Both the above described methods of erasing, A and B can be used with this operation 2. However, it is also possible to erase the charge pattern by grounding the writing gun cathode 25 (Figure 2), so that the Writing beam, when it is now scanned over the target surface, will bring both the charged and the uncharged target areas to cathode potential, since the writing beam will strike the target surface with a velocity at which the secondary emission ratio is less than 1. In erasing the target with the writing gun, it is not necessary to use a sharp focus of the beam on the target but the beam can be defocused and scanned over the target. Also, the writing gun potential can be adjusted to provide a broad beam of electrons covering all of the surface of the target.

Holding so that the areas of the target surface which have been charged to around 20 volts positive are struck by the beam with an energy which is above first cross-over, while the uncharged areas at substantially ground potential will be struck by the beam below first cross-over.

As indicated in Figure 1 by the dotted circuit 59, it is possible to collect the output signal from the tube from the collector mesh screen 34. In the charged or positive areas of the foraminous target 16, the reading beam electrons will pass through the target to the collector screen 34 as described above. These reading beam electrons collected by screen34 can constitute the output signal pulses of the tube by connecting the collector mesh screen 34 into the amplifying circuit 59.

OPERATION 3 Screen 34 may be connected to the input amplifying circuit connected to the tube so that incoming signal pulses are applied to the collector screen 34 while the writing beam is scanned over the target surface. During amplified so that the maximum signal will swing grid 34 to either 20 volts positive with respect to ground or to 1-50 volts positive with respect to the ground. Thus, the writing beam will maintain the target areas that it strikes at ground when there is no signal on screen 34. But-with a signal pulse on the screen the writing beam and 'simul'taneou'sly scanned establish .a cliarge pattern thereon; "The secondary elecwill drive the dielectric target surface to whatever potential" the collector .screen 31? is raised by the input isignal. Thus, there is established on the target. surface acliarge pattern varying from ground to 20 volts positive in one case or from-ground to 100" to 150volt's p'ositivointhe other case. Theholding and erasing techniques described abovef or'Operations 1' and 2} may be used'in the operation of the tube under these conditions wherever applicable; Slow erasure 7 Another methodof slow' erasureisdisclosed'in the tube ofi Figure: .As the reading. beam-electrons which penetrate screen; 16- strike screen :34, a: cert-ainrnumber-of sec- .ondary electrons are initiated. These electrons normally are urged by the positive field: of. wallaiilthrough screen:

34- and:are collectedby the variouspositive electrodes of the tube. However,v itis possible to redirect these secondary electrons from: screen 34 onto target 16'bylower' ing the voltage ofithe'wall. 32..- These secondary electrons slowly drive the target surface; toward ground potentiaL. A disadyantage of this particulartprocedureishowever, that in changing the'voltage of electrode- 321 the writing beamis detocusedrand. requires: that the fieldofi-coil 38 be readjusted toreestabli shathe focus of; the beam. Furthermore changingv the field. of. coil..38 will. defocus the:

. reading beam of gunl26'. more satisfactory arrangement is to provide an additional screen 59,.n1ountedbetween gun.24 and the: collector. screen. 34. and independent of the wall electrode. 32'. .Duringnormal tube operation,

screen 59 may be given the same. potential as: the walla el'ectrQdeSZ which 'is'around some ZOU vol'ts positive with striking, the target.

Picture storage .tuI Je amiiious'm'etal. sheetlor screen coatedwith a thin filnr of silica asidescribedabove for target.1'6 of Figure l, and maybe a, 230 mesh, stainless steel. woven screen coated with a thin film oflsilicav Between target 66 andthe photocathode filnr'64 is mounted a tubular accelerating electrode 68 supporting alii'ghtransmission screen 63 adjacent the plate cathode. 64,. for directing,v photoelectrons from. surface 64toward; targetv66l A..focusing..coil. 72 is mounted coaxially to .andsurrounding-the tube envelope 601, The. magneticffielcL-provided by coil'lllmaintains the photoemli'ssionf'romfilmlfl insnbstantially parallel paths ,greater. detail. Briefly, the reading. gun- 80 comprises a cathode.- structure-=82, control grid 84 and accelerating respectlt'o groundl. However for slow erasure the screen 59"may 'be'loweredto a potential which will suppress the secondary electrons from screen 34 and urge them toward the target electrode I6. The use .of screen 59..thns2. 1 eliminates. the complications of .deilocusing the electro beams ofthe tube. I

Half-tonabpemtionr As described" above, any surface of targer'ld struck by electrons of the writingibeam is' driven positively to equilibrium or collector screenpotentiali Under these conditions, the reading beam will resolveall charged areas of target 16 by equal signal values. However if the writing beamis modulated with-signal voltages ranging up wards from cutofipotential, it is possible to establish a range of charges on target 16 from a minimum; at ground potential, to -amaximum near collector screen potential.

' The reading beam then can resolve such intermediate potentials onthe target to provide half-tone; signal pulses the output circuit.

To provide haif t'one operationof the tube'of" Figure I 1, use is made of the velocity distribution range ofthe'readi'n'g' beam electrons. The potential of screen 34" is adjusted to a positive value of" afew volt's above'ground.

The writing gun is modulated by the incoming signals over the target surface to from emission from each elemental area: of the target surface will beproportiona'l tothe number of primary writiug beam electrons-strilcingthe respective area. v

'Th e D. C. grid bias'of the writing gun is chosenso-that,

K when the rno'dulatingsignal makes it a maximum, the

. beam can :charge 'the-target capacity under the beanr i'n' -a "positive direction to slowest electrons of a potential sufiicient to allowthe the reading beam topenetrate the target; As the modulating signal becomesincreasingly more negative; fewerwrit-ingbeam electrons are available don-changing the target; Thcpotential swing of the target thnszbecomes eversmallerand' fewer reading beam electronstcanipenetrate -the targeta a That; port-ionof the reading beam returned to' gun Z'4 will then be modulated in accordance to the range of potentials' on target 16 to provide" half-tone signals in the output eircuit of the tube.

iii-its passage to..target 66.. A. secondary electron collector screen 74' mounted closely adjacent. to. target 66 by a support ring 76. Collector screen-74.corresponds in function to collector 34 of Figure l.

The reading portion of the tube of Figure 6 is substantially same iasathat. described. int Figure 1 However, thewgun portions and. the multiplier section? are-shown-in cent target .66.. Screen.92 corresponds to screen 41L of Figure I. The electron beam of gunis scanned-over the target surface by deflecting. coils. represented. by the neck yolie97 Focusing. coil: 7i extends tongun' 80 :and provides. a magnetic focusing fieldof the. beam of; gunfil ontothe surface of target 66.. V The several electrodes-of the .tuheare .operatedat the voltages shown in Figure 6. These voltages are notlimiting but are representative of. those whioliha ebeemused in a tube. of this type. The beam .OfIgunBDlscans-the silica coated-surface. of the .fbrami'nous target 66 forcing: gun 80 to drive that surface to substantiallyground. on gun cathode potential- At thisipotential', theisurfaceof target 66 reflects the remainingportion .ofthc beam baclc toward gun 80. The reflected portionof'the reading beam strikes the surface of accelerating electrode- 88 with suflicient energy to provide secondary emission therefrom, which is 'direct'ed'by .apersuader electrode 93 into. a multiplier section '94 surrounding gun 80. Multiplier 94" is of the type. set forth in the above cited patentf ofIPauYKQW'eimer and consists of. 5 stages of amplification. The collector electrode 95 off theimultiplier 94 is substantially a fine mesh screen connected into an amplifying circuit represented by'a tube 96. I V

' Writing The tube of Figure 6 is one whichestablished a charge pattern on target6 6' corespondingto an optical image projected uponrthe photocathode filmr'itr iiheoptical'limage may he of any type desired. Photoelectrons are emitte'dz'fromi the lightednareasofi film 64 andare accelerakaejrie l 1 light pattern focussed upon the photocathode 64. This, then establishes a charge pattern on the target 66, which closely corresponds to the light pattern focusse'd upon the photocathode.

Reading The charge pattern established on target 66 may be continuously read by the beam of gun 80, in the manner described above for the tube of Figure 1. The output signal from the multiplier electrode 95 may be utilized to drive an oscilloscope or picture tube 50 that a visual image may be produced of the charge pattern stored on target 66. This visual picture can be maintained and observed for any desired length of time. The output signal may be removed at the collector screen 74 also, as the electrons of the reading beam which have penetrated the target screen are largely collected by this screen (74).

Erasing The charge pattern on target 66 can be erased by changing the potential of collector screen 74 to ground so that all secondary emission from the target 66 is suppressed and caused to fall back onto the target surface to drive the surface back to ground potential. In this operation, a uniform light may be directed onto photocathode 64 so that a uniform photoemission will fall on all the target surface to erase the charge pattern.

Holding potential and the uncharged areas of the target screen at below first cross-over. pattern on target 66.

Another holding technique is that in which the potential of screen 74 is maintained above first cross-over potential relative to ground during writing. Then reading" beam electrons passing through both target screen 66 and collector screen 74 will be repelled by the zero potential field surface in front of the photocathode. Some of these repelled electrons will get back to the target 66 and will be drawn over to the charged target areas to strike at above first cross-over to restore them.to equilibrium or collector screen potential. Those electrons falling on the uncharged areas will .be below first cross over and will maintain these areas at ground.

The tube of Figure 6 may be operated at different sets of electrode potential from that indicated in the figure. For example, a tube of the type of Figure 6 was operated with the photocathode 64 at minus 540 volts relative to ground, the accelerating electrode 68 and collector screen 74 at between 24 and 100 volts positive; the target 66 at ground; decelerating mesh 92 at 210 volts positive; wall electrode 90 at 170 volts positive; persuader electrode 93 at 204 volts positive; gun accelerating grid 86--88 at 213 volts positive. The field of coil 72 was adjusted to substantially 8O gauss.

Half-tone operation If the optical image is maintained for any length of time on photocathode 64, all areas of target 66 struck by photoelectrons will be driven positively to the equilibrium potential established by collecting screen 74. Those areas of target 66 charged by photoelectrons from partially illuminated areas of the photocathode 64 are charged as high as those target areas charged by photoelectrons from brightly illuminated portions of the photocathode. The reading beam, in this case, will resolve the charge pattern and provide as great a signal from those areas charged by photoelectrons from bright areas of the photocathode as the signal obtained from those areas of the target This will reestablishthe charge charged by photoelectrons from partially illuminated or gray areas or half-tones of an image projected on photocathode 64.

To provide half-tone operation of the tube of Figure 6, the optical image projected on photocathode 64 may be only allowed to fall on the tube instantaneously so that the photoemission from the partially illuminated or gray areas of the photocathode is not enough to charge the corresponding areas of target 66 to equilibrium potential, but only to a potential between ground and equilibrium. The reading beam now will lose electrons through target 66 in proportion to the amount of charge on the target areas adjacent the apertures. The return beam to gun 80 will be thus modulated in amount corresponding to the charge established on each area of the target.

Another mode of tube operation to provide half-tone signals is by lowering the potential of accelerating electrode 68 to a point at which reading beam electrons passing through target screen 66 are in part returned to the charged areas of target 66, to drive them down toward ground potentiaL- If the optical picture is maintained on photocathode 64, potentials of screen 74 and of electrode 68 can be found which will return just enough reading beam electrons to those target areas, charged by photoelectrons from the partially illuminated areas of the photocathode, that the potential of these target areas will v emissive cathode for establishing a charge pattern on saidv remain below equilibrium potential. Conditions'can be set so that the secondary emission from those target areas charged by photoelectrons from the brightly illuminated areas of the photocathode 64 is just great enough to raise these target areas to equilibrium potential in spite of reading beam electrons falling back on these bright areas. Thus there is established on the surface of target 66, facing the photocathode 64, a charge distribution varying in potential, from point to point, from reading beam cutoif to equilibrium potential. The reading beam returned to the multiplier 94 will be modulated in accordance to the charge pattern and, thus, resolve the half tones or gray areas of the optical pattern projected on photocathode 64.

What is claimed is:

1. An electron discharge device comprising, a foraminous target electrode sheet having one surface of electrically insulating material, means including an electron insulating target surface, an electron gun spaced from said cathode for forming a beam of electrons, means for scanning said beam over the other surface of said target electrode, and an electrode for collecting beam electrons reflected from said target.

2. An electron discharge device comprising, a foraminous target electrode sheet having one surface of electrically insulating material, an electron gun to provide an electron beam for establishing a charge pattern on said insulating surface of said target, said electron gun including a cathode and a control grid electrode spaced from said target electrode, electrode means between said cathode and target electrode fordirecting beam electrons from said cathode onto said insulating surface with energies sufliciently large to provide a secondary emission greater than unity from said insulating surface, a first deflecting means for scanning said beam over said target and a collector electrode adjacent said insulating surface of said target to collect secondary electrons from said insulating surface, lead means from said cathode and said control grid electrode to be connected to a signal source for applying signal voltages thereto to modulate said electron beam, means spaced from said target electrode and including an electron source for directing a second beam of electrons adjacent to the charged target surface, a second deflection means positioned between said electron source and said target for sequentially scanning said second beam to different portions of said target to be modulated thereby, and an electrode for collecting said second modulated electron beam.

"3. An electron discharge device 'compri'singa fol-aminous target electrode sheet having one surfacerof electrically insulating material, means including an electron emissive cathode for establishing-a charge pattern on said insulating target surface, an electron .Jgu'n spaced from said cathode including a second cathodefor-"forming a beam of electrons, means for scanning said beam over i coated target-surface, said means including a source of electrons and electrode means between said electron source and said target sheet "for directing electronsfrom said source onto said coated target surface with energies su'fliciently great to provide a secondary emission greater than unity from said target surface, an electron gun spaced from said target sheetjforforming a beam ofelectrons, means for scanning said beam over the other surface of said target sheet, an ,electrodefor ,collectingbeam electrons from said target electrode, a screen reflector "mounted between said target electrode andsaid electron source ,for repelling said secondary and beam-electrons towardsaid coated target surface.

.5. A charge storage device comprising, a target telec- =trodeincluding a conductive formaminoussheet, ianelectrica'1ly insulating material coating one surface of said target sheet, means for establishing a charge pattern on :said coated target surface, said means including a source of electrons and electrode means between said electron source 'and said target sheet for directingelectrons from said cathode onto said coated target surface with energies sufliciently great to provide a secondary emission greater than-.unity. from said target surface ran electron gun spaced from said electron source for forming a beam of electrons, means for scanning said beam over the other surface of said target sheet, an electrode for collecting beam electrons from said target electrode, a

screen mounted between said target electrode and said electron source for collecting secondary electrons from said coated target surface, and lead means connected to said screen for connecting to a signalsource for applying signal voltages thereto for modulating the collection of secondaries from said coated targetisurface.

6. -A charge storage device comprising, a targetelectrode including a. foraminous sheet "having an electriictxlly insulating coating over the surface thereof, an electron gun spaced from said target electrode for providing an electron beam for establishing a charge pattern on one surface of said foraminous sheet, electrode means between said electron gun and said target for directing the electron beam from said gun onto said target surface at energies sufliciently great to provide secondary electron emission from said target surface, means for scanning the electron beam from said gun over said target surface, a screen electrode closely spaced from said target surface for collecting the secondary electrons therefrom, and holding means for maintaining the charge pattern on said target surface, said means including said electron gun, said screen electrode and a mounting ring suppporting said target sheet across the open center of said ring,

said mounting ring having a portion thereof exposed to the scanning of said electron beam, lead means connected to said mounting ring for joining said ring to an electron source whereby occurs upon bombardment of said ring by electrons said gun.

a secondary electron emission from .7..An electron discharge device comprising, a target electrodeincluding aforaminous shcetandlan electrically insulating coatingon the surface of one side of said target sheet,- -means for establishing a charge pattern .on the coated surface of said "target sheetyane'lec'tron gun facing the other ."side of said tar -get sheet for forming a""beam of electrons, scanning -me'ans for directing the electron beam over said target sheet, a screen mounted ."clos'e'ly adjacent said one ,side of said target sheet for .directing beam electrons onto said coated target surface to erase said charge pattern.

'8. An :electron discharge device comprising, a target electrode including 'aifine mesh conductive screen and an electricallyinsulatirrg coating on the surface of one side "of said screen, means including a cathode electrode spa'ced'fr'om said target electrode for establishing a charge pattern on the coated-surface of said target screen, said means including .an accelerating electrode between said cathode and target electrodes for directing electrons from said source onto said coatedtarget surface with energies sufliciently great toprovide secondary emission from said coated .targetsurface greater than unity, ;an

electron gun-facing the other side of said target screen "for forming abeam of electrons directed at said other screen side, 'a'second screen mounted adjacent and facing said one side of said 'taifgetscreen for collecting the sec- 'ondary emission from said coated target surface, and lead means connectedto said. second screen for connectin'g said second .s'creento a low fpotential'to return the secondary emission to said coated target surface for erasing the .charge .pattern thereon.

"9. An electron discharge fdevice comprising, a target electrode including "a "fine mesh conductive screen and and insulatingcoating on the surface of one side of said screen, means including a cathode electrode "spaced from said target "electrode'forestablishing a charge pat tern on the :coated surface or said "target screen, said means. including an accelerating "electrode between said ;cathode;and target electrodes for-directing electrons from :said cathodeonto said coated target surface with energies sufiiciently great to provide secondary"emissionfrom said coated target surface greater than unity, L311 "electron gun .including an 'ele'ctrongsource "facing the other side of said target screen "forforrning a "beamof electrons directed at said "other screen side, "lead means-connected to said cathode electrode, said electron source-and-said conductive screen to join them .to sources of substantially the same potential-to hold said chargepattern onsaidtarget electrode.

10. A charge storage device comprising, a target electrode including a conductive foraminous sheet, an insulatingmaterial coating one surface of saidtarget sheet,

means :for establishing 'a charge 'pattern "on said coated .target surface, said means includinga sourceo'f'electrons "and electrode meansbetweem'said electron source and said target sheet for directing electrons from said source onto said coated target surface with energies sufficiently great to provide a secondary emission greater than unity from said target surface, an electron gun for forming a beam of electrons, means for scanning said beam over the opposite surface of said target sheet, an electrode for collecting beam electrons reflected from said target electrode, a first screen mounted between said target electrode and said electron source collecting said secondary electrons, and a second screen mounted between said first screen and said electron source for reflecting beam electrons passing through said first screen back onto said charged target surface.

11. An electron discharge device comprising, a foraminous target electrode sheet having one surface of insulating material, means including a photoemissive cathode for establishing a charge pattern on said insulating target surface, an electron gun spaced from said photoemissive cathode for forming a beam of electrons, means for scanning said beam over the other surface of said target 15v electrode, and an electrode for collecting beam electrons from said target.

12. A charge storage device comprising, a target electrode including a conductive foraminous sheet, an insulating material coating one surface of said target sheet, means for establishing a charge pattern on said coated target surface, said means including a photocathode and electrode means between said photocathode and said target sheet for directing electrons from said photocathode onto said coated target surface with energies sufficiently great to provide a secondary emission greater than unity from said target surface, an electron gun spaced from said photocathode for forming a beam of electrons, means for scanning said beam over the other surface of said target sheet, an electrode for collecting beam electrons from said'target electrode, a screen mounted between said target electrode and said photocathode for collecting secondary electrons from said coated target surface.

13. An electron discharge device comprising, a foraminous target electrode sheet having one surface of insulating material, means for establishing a charge pattern on said insulating surface of said target, said means including a photocathode spaced from said target electrode, electrode means between said photocathode and target electrode for directing electrons from said photocathode onto said insulating surface with energies sufficiently large to provide a secondary emission greater than unity from said insulating surface, and a collector electrode adjacent said insulating surface of said targetto collect secondary electrons from said insulating surface, an electron gun spaced from said photocathode for forming a beam of electrons, means for scanningsaid beam over the other surface of said target electrode, and an electrode for collecting beam electrons from saidltarget.

14. The method of operating a storage device including a foraminous target electrode sheet having an electrically insulating coating on one surface of said foraminous sheet, said method comprising the steps of establishing a charge pattern on the insulating coating of said target sheet, scanning the other surface of said target sheet with a beam of electrons having low velocities in the region of said target, repelling electrons of said beam penetrating through said foraminous target back onto said insulating coating to erase said charge pattern thereon. 1

15. The method of operating a storage-device including a foraminous target electrode sheet having an electrically insulating coating on one surface of said foraminous sheet, said method comprising the steps of, establishing a charge pattern on the insulating coating of said target sheet, directing electrons onto said target sheet with energies sufficiently great to provide a secondary electron emission greater than unity from said 16 insulating coating, repelling said secondary electron emission back onto said insulating coating to erase the charge pattern thereon.

16. The .method of operating a storage device including a foraminous target electrode sheet having an electrically insulating coating on one surface of said foraminous sheet, said method comprising the steps of, establishing a charge pattern of both high and low relative potentials on said insulating coating of said target sheet, scanning sequentially over a portion of said charged insulating coating electrons having energies suflicient to provide a secondary electron emission of less than unity from portions of said insulating coating at low potentials and a secondary electron emission greater than unity from portions of said insulating coating at high potentials whereby the charge pattern is maintained on said insulating coating.

17. An electron discharge device comprising, a foraminous target electrode sheet having one surface of electrically insulating material, means including a first electron emissive cathode for establishing a charge pattern on said insulating target surface, an electron gun spaced from said cathode including a second cathode for forming a beam of electrons, means for scanning said beam over said target electrode, lead means connected to said target sheet for connecting to a potential source whereby said target sheet is maintained near the potential of said second cathode and electrode means for collecting beam electrons reflected from and transmitted through said foraminous target.

18. The method of operating a storage device including a foraminous target electrode sheet having an electrically insulatingcoating onone surface of said foraminous sheet, said method comprising the steps of establishing a charge pattern on the insulating coating of said target sheet, scanning said target sheet with a beam of electrons having low velocities in the region of said target, repelling electrons of said beam penetrating through said foraminous target back onto said insulating coating to erase said charge pattern thereon.

References Cited in the file of this patent UNITED STATES PATENTS 2,182,578 Blumlein et al. Dec. 5, 1939 2,259,507 Iams -2 Oct. 21, 1941 2,263,032 Farnsworth Nov. 18, 1941 2,458,205 Rose Jan. 4, 1949 2,503,949 Jensen et al. Apr. 11, 1950 2,532,339 Schlesinger Dec. 5, 1950 2,540,623 Law Feb. 6, 1951 2,547,638 Gardner Apr. 3, 1951 2,549,072 Epstein Apr. 17, 1951 2,667,596 Szegho et al. Jan. 26, 1954 

